This invention relates to a brake system for automotive vehicles, which is provided with a master brake cylinder and with a working piston confining a working chamber and communicating with at least one pressure chamber of a wheel brake. The system is provided with a power booster connected upstream of the master brake cylinder and connected to an auxiliary energy source for the purpose of pressure supply.
A brake system featuring the above characteristics is described in prior patent application no. P 33 15 731.6. In the brake system according to the prior suggestion a recharge of the pressure medium accumulator is impossible during a brake application after there has been a discharge of the pressure medium accumulator so that the entire auxiliary energy provided by the pressure medium pump directly reaches the hydraulic brake booster. In this described brake system it is considered less advantageous that, the more the foot pressure at the brake pedal increases, the more the booster piston is acted upon which is supplied with pressure by the auxiliary energy source and the more the pressures increase in the working chambers which, on their part, cause an increased expansion of the brake system components acted upon by the pressure. This also implies a corresponding increase in the respective travel of the individual working pistons and of the booster piston. However, as the travel of brake pedal also inreases as the respective travel of the working pistons and of the control piston increase the result may be that there is only a very small travel reserve at the brake pedal when high pressures are required.
This is of particular disadvantage when there is, for example, a failure of one brake circuit of a tandem master cylinder. In that case, in order to build up a pressure the respective working piston of the defective working chamber must be displaced over its full travel until it comes to a stop at the working piston in front of itself or a fixed abutment formed with the housing. In this instance, the travel at the brake pedal may become so large that there will be insufficient travel reserve if a sufficiently high hydraulic pressure in the brake system must be generated. Even if the remaining brake pedal travel would just suffice to generate the required pressure in the brake system, the driver would nevertheless be of the impression of a total failure of the brake system due to the very large brake pedal travel, the driver will no longer believe that braking the vehicle is possible with so long a brake pedal travel.
It is thus an object of this invention to further develop a brake system of the type described in such a manner as to ensure that, after a predetermined pedal travel, the brake pedal travel will not increase any further, with the brake pedal pressure and the braking pressure continuing to increase.